Apparatus for displaying distance reference marks on a radar screen

ABSTRACT

Apparatus for simultaneously producing an adjustable distance reference mark and fixed distance reference marks on the display device of a reflected-beam position-finding system. The apparatus includes a pulse generator for producing timing pulses, a pulse counter for counting the timing pulses and producing a digital output indicative of the count, a manually adjustable selector for producing a marking pulse each time the counter produces a digital output indicative of a particular preselected count and means for producing further marking pulses each time the counter produces a digital output indicative of a particular fixed count. The marking pulses produced are employed to cause the display device to display a mark indicative of a particular preselected distance and marks indicative of particular fixed distances.

ite States atent Scireer APPARATUS FOR DISPLAYING DISTANCE REFERENCEMARKS ON A RADAR SCREEN Inventor: Kurt Scheer, Bremen, Germany Fried.Krupp. Gesellscllaft mlt besclirankter llall'tung, Essen, Germany Filed:July 10, 1969 Appl. No.: 840,656

Assignee:

Int. Cl ..Gls 7/22 Field of Search ..343/ EM, 5 PP, 11, I3

References Cited UNITED STATES PATENTS Miller ..343/13 X 10/1958 Nagel..343/13 Feb. 29, 1972 2,975,413 3/1961 Landee et al. ..343/5 E XFOREIGN PATENTS OR APPLICATIONS 349,309 1 1/1960 Switzerland ..343/5 E XPrimary Examiner-Malcolm F. l-lubler AttorneySpencer & Kaye [57]ABSTRACT Apparatus for simultaneously producing an adjustable distancereference mark and fixed distance reference marks on the display deviceof a reflected-beam position-finding system. The apparatus includes apulse generator for producing timing pulses, a pulse counter forcounting the timing pulses and producing a digital output indicative ofthe count, a manually adjustable selector for producing a marking pulseeach time the counter produces a digital output indicative of aparticular preselected count and means for producing further markingpulses each time the counter produces a digital output indicative of aparticular fixed count. The marking pulses produced are employed tocause the display device to display a mark indicative of a particularpreselected distance and marks indicative of particular fixed distances.

8 Claims, 3 Drawing Figures till I nlun lllllll PULSE STAGE (cau/vrERggfi Hllllllll HHIIIIII 11mm n W W 158 PREsstEcroR BACKGROUND OF THEINVENTION The present invention relates to apparatus for producing anadjustable reference or scale mark on the screen of a positionfindingsystem (e.g., sonar or radar) which operates according to the reflectedbeam principle.

Apparatus for producing an adjustable scale mark on the screen of adisplay device (e.g., a cathode-ray tube) of a radar system is known inthe art. This prior art apparatus comprises a time delay pulse sourcewhich is triggered by the transmission ofa radar beam pulse. Such timedelay pulse sources have employed adjustably analog delay circuits whichhave the disadvantage of limited accuracy due to the unavoidabletolerances and the temperature-dependent behavior of electrical circuitelements. Although the official standards of accuracy (normally :1percent) may be achieved with these devices, even this magnitude oferror always leads, in practice, to annoying deviations between thepositions of the adjustable scale marks and fixed scale marks when theradar system is additionally provided with apparatus to producenonadjustable calibrating distance scale marks on the display device.

In order to maintain the error as small as possible, it is conventionalto avoid sweeping through the entire display range of the radar systemin a single traverse, and rather to operate the analog scale markgenerator together with the display device within selected distanceranges. However, even in this case, though the error is reduced, it isnot eliminated. The disturbing differences between the adjustable andfixed scale marks continues to remain.

SUMMARY OF THE INVENTION An object of the present invention, therefore,it to provide apparatus of the type described above which can produceboth the fixed and the adjustable distance reference marks with exactlythe same scale so as to eliminate the annoying deviations between thepositions of these two distance displays.

This object, as well as other objects which will become apparent in thediscussion that follows, is achieved, according to the presentinvention, by constructing the time delay pulse source as a pulsegenerator for producing timing pulses; a pulse counter for counting thetiming pulses and producing a digital output indicative of the count;and a preselector, connected to receive the digital output, forproducing a marking pulse each time the counter reaches a particularpreselected count.

It is convenient if the preselector is provided with a digital indicatorfor displaying the preselected count.

Accordingly, when the preselected count is reached, the resultingmarking pulse will gate the display device to display a mark indicativeofa particular preselected distance. Since the timing pulses from thegenerator as well as the pulse counter can also be employed to producethe fixed distance reference marks, deviations between the fixed and theadjustable distance marks can be eliminated. The magnitude of error inthe distance display will consequently only depend upon the accuracy ofthe timing pulse generator which can be stabilized to within any desireddegree of accuracy using techniques already known in the art. As anexample, the timing pulse generator can be stabilized by means ofaquartz crystal.

According to one preferred embodiment of the present invention, both thetiming pulse generator and the transmitter of the position-findingsystem can be simultaneously gated by a control device to provide thedesired synchronous operation. According to another preferred embodimentofthe present invention, the timing pulse generator is allowed tooperate continuously. The transmitter is synchronized by means of acounter which periodically gates the transmission of a beam upon receiptfrom the pulse generator of each nth timing pulse.

According to a third preferred embodiment of the synchronizing circuitaccording to the present invention, there is provided a primary pulsegenerator which produces primary timing pulses with a period that is awhole-numbered fraction of the period of the timing pulses ultimatelyused to define a unit of distance. These primary timing pulses aresupplied to a digital counter through a gate which is opened by a pulsefrom a synchronizing control device. After m primary pulses have beenreceived by the digital counter, the same produces the ultimate timingpulses.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of apparatusaccording to a preferred embodiment of the present invention forproducing one adjustable and several fixed distance scale marks on thescreen of the cathode-ray tube display device of a reflected beamposition-finding system.

FIG. 2 is a block diagram of a modified synchronizing circuit which maybe used in the apparatus of FIG. 1.

FIG. 3 is a block diagram of another modified synchronizing circuitwhich may be used in the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of thepresent invention will now be described in connection with FIGS. 1 to 3of the drawings. FIG. 1 of the drawing illustrates one preferredembodiment of apparatus for producing both an adjustable and severalfixed distance reference marks on the screen of the display device of aradar system. The radar system is provided with a single antenna 1 whichserves to transmit the outgoing radar beam pulses as well as to receivethe reflected beam pulses. The antenna 1 continuously rotates about avertical axis in order to scan the entire surrounding region. Thereceived reflected beam pulses are employed in the conventional mannerto produce a display on a display device; for example, on the screen 2of a cathode-ray tube. The cathode-ray tube is provided with adeflection system which rotates in synchronism with the rotation of theantenna so that the angular position of the echoes displayed on thescreen will correspond to the bearing of the reflecting objects ortargets. The beam of the cathode-ray tube will also be deflected in theradial direction in synchronism with the transmitted radar beam pulses,e.g., by a sawtooth generator, so that the distance from the center ofthe screen to the echoes displayed thereon will correspond to thedistance of the reflecting objects. Such a display is known in the artas a plan position display.

In the embodiment illustrated in FIG. 1, gate pulses are generated in acontrol device 3 and employed in the conventional manner to control thetransmitter 4. These gate pulses are also sent through a line 5 to agating stage 6 which controls a pulse generator 7 that produces timingpulses u The period between these timing pulses 14, corresponds timewiseto the smallest unit of distance to be measured; for example 0.1nautical miles or 0.1 kilometers.

The gating stage 6 delivers the necessary control voltage to the pulsegenerator and contains the delay device to adjust the correct timerelation between the transmitted pulse and the timing pulses as isconventional in the art.

By counting the timing pulses a in a suitable pulse counter 8, it ispossible to generate a pulse for producing scale marks indicative of anydesired distance in steps which correspond to the smallest unit ofdistance to be measured. These distance scale marks will be repeatedlygenerated with every sounding period so that in the course of one ormore revolutions of the cathode-ray beam the individual marks willproduce a distance scale ring E on the screen 2.

The position or diameter of the distance scale ring E is controlled byproducing a marking pulse when the pulse counter 8 reaches a preselectedcount. This preselection is effected by a digital preselector 9.Assuming, for example, that an object Z is noted on the screen of thecathode-ray tube at a distance between 20.0 and 40.0 natical miles, itsdistance can be ex- .ictly determined by adjusting the preselector 9until the distance ring E so produced passes through the luminous pointrepresenting the object Z. This adjusted distance may then be read froma digital indicator 10 which is coupled with the preselector 9 todisplay the selected distance.

As is shown in FIG. I, the preselector 9 is connected to receive signalsfrom each of the decade stages of the pulse counter 8 and to pass onlyone signal from each decade stage to an AND-gate II. When the decades ofthe pulse counter 8 are each in a state selected by the preselector 9, asignal will be present at all the inputs of the AND-gate 11 causing thisgate to generate a pulse it This pulse L4,, is employed in theconventional manner to gate the beam of the cathode-ray tube andtherefore produce a point of light, or scale mark, on the screen 2.

The timing pulse generator 7 is also employed to produce fixed distancescale or calibration marks on the screen of the cathode-ray tube, forexample at the distances 20.0, 40.0 and 60.0 nautical miles in the60-mile range as shown in FIG. I. The use of this common pulse generator7 ensures that the scale for the fixed and for the adjustable distancereference marks, which form the distance rings E, will coincide.

In the embodiment shown in FIG. 1. the timing pulses 14 are passedthrough an AND-gate 13 to the first decade of the pulse counter 8 assoon as the gate 13 is opened by a gating pulse applied to its inputline 14 by the control device 3. The leading edge of this gating pulseappears at the moment when the transmitter 4 sends out a beam on theantenna 1. The marking pulses u and u, which produce the fixed scalemarks on the cathode-ray tube screen are generated in a manner identicalto the adjustable scale marking pulse u by connecting the inputs ofrespective AND-gates 15, I6 and 17 to suitable decade terminals of thepulse counter 8.

With the illustrated counter it is possible to sweep the entire distancerange. In contrast to the analog methods used in the prior art, it isunnecessary to switch to various ranges of measurements (e.g., from 0 to200 nautical miles or from O to 60.0 nautical miles) to reduce theerror.

Since the period of the timing pulses 14, corresponds to the smallestunit of the distance to be measured (e.g., 0.1 nautical miles), meansmust be provided to ensure synchronism between the timing pulses a andthe transmitted pulses of the radar system. In the first embodimentofthe present invention, illustrated in FIG. I, this synchronism isachieved by gating the timing pulse generator 7 through the gating stage6.

FIG 2 illustrates a second preferred embodiment of this synchronizingcircuit which may be employed in the apparatus of FIG. 1. In thisembodiment the pulses produced in the control device 3 are synchronizedby a counter 18 which produces an output control pulse upon receipt of agiven number (n) of the timing pulses u, from the continuously runningtiming pulse generator 7,

FIG. 3 shows still another embodiment of a synchronizing circuit whichmay be employed in the apparatus of FIG. 1. This circuit is providedwith a primary timing pulse generator 7 which produces primary timingpulses in, with a period which is a whole numbered fraction of theperiod of the timing pulses 14,; that is. a fraction of the periodcorresponding to the smallest unit of the distance to be measured. Theseprimary timing pulses u,, are applied in quick succession to an AND-gate 19 which is opened by a gating pulse a produced by a control device3. The pulses r4 which pass through the AND- ,gate 19 are repeatedlycounted by a digital counter 20. This counter 20 produces the timingpulse u that serves as the timmg pulse for the distance determination.after a prescribed number of pulses 14 have been received.

in each of the embodiments illustrated in FIGS. 1, 2 and 3 the pulsecounter 8 is cleared (reset to zero) at the end of the display time bythe gating pulse or its trailing edge produced by the control device 3.

it will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations. In particular, the present invention is not limited to usein radar systems but can also be employed,

for example, with sonar systems which operate with underwater sound.

lclaim:

1. Apparatus for simultaneously producing fixed distance reference marksand an adjustable distance reference mark on the display device ofareflected beam position-finding system, comprising, in combination:

pulse generator means for producing timing pulses spaced with a periodequal at most to the smallest time interval which is to be adjusted;

pulse counter means, connected to the output of said generator means,for counting said timing pulses and producing a digital outputindicative of the count in said counter means;

means for causing said pulse counter means to begin counting said timingpulses when said position-finding system transmits a beam pulse;

adjustable preselector means, connected to said counter means forproducing a first marking pulse each time said counter means produces adigital output indicative of a particular, preselected count;

means, connected to said pulse counter means, for producrng secondmarking pulses each time said counter means produces a digital outputindicative of preset fixed counts of said timing pulses; and

means connecting the outputs ofsaid preselector means and said secondmarking pulses producing means to said display device for causing saiddisplay device to display a mark in response to each of said first andsecond marking pulses whereby the mark displayed in response to saidfirst marking pulse is indicative of a particular adjustable preselecteddistance and the marks displayed in response to said second markingpulses are indicative of particular fixed distances.

,2. The apparatus defined in claim 1, wherein said preselector meansincludes digital indicator means for displaying said preselected count.

3. The apparatus defined in claim 1, wherein said means for causing saidpulse counter to begin counting comprises means, connected to said pulsegenerator means, for starting said pulse generator means each time saidposition-finding system transmits a beam pulse.

4. The apparatus defined in claim 3, wherein said positionfinding systemincludes a transmitter means, connected to said starting means, fortransmitting the beam pulses and wherein said starting meanssynchronously gates said transmitter means and said pulse generatormeans.

5. The apparatus defined in claim 1, wherein said positionfinding systemincludes a transmitter means for transmitting the beam pulses, andwherein said means for causing said counter means to begin countingcomprises a second pulse counter means, connected to said pulsegenerator means and to said transmitter means, for synchronously gatingsaid transmitter means upon receipt of the nth timing pulse from saidpulse generator means.

6. The apparatus defined in claim I, wherein said timing pulses arespaced with a period corresponding to the smallest unit of distance tobe displayed on said display device.

7. The apparatus defined in claim 1, wherein said pulse generator meansincludes:

l. a primary pulse source means for producing primary pulses spaced witha period substantially smaller than said period of said timing pulses;

. gating means, connected to said primary pulse source means, forpassing said primary pulses upon receipt of a gating pulse; and

. third pulse counter means, connected to said gating means, forproducing said timing pulses upon receipt of the mth primary pulse fromsaid gating means.

8. The apparatus defined in claim 7, wherein said position findingsystem includes a transmitter means for transmitting the beam pulses,and wherein said means for causing said counter means to begin countingcomprises control means, connected to said transmitter means and to saidgating means, for synchronously gating said transmitter means and saidgating means.

1. Apparatus for simultaneously producing fixed distance reference marksand an adjustable distance reference mark on the display device of areflected beam position-finding system, comprising, in combination:pulse generator means for producing timing pulses spaced with a periodequal at most to the smallest time interval which is to be adjusted;pulse counter means, connected to the output of said generator means,for counting said timing pulses and producing a digital outputindicative of the count in said counter means; means for causing saidpulse counter means to begin counting said timing pulses when saidposition-finding system transmits a beam pulse; adjustable preselectormeans, connected to said counter means for producing a first markingpulse each time said counter means produces a digital output indicativeof a particular, preselected count; means, connected to said pulsecounter means, for producing second marking pulses each time saidcounter means produces a digital output indicative of preset fixedcounts of said timing pulses; and means connecting the outputs of saidpreselector means and said second marking pulses producing means to saiddisplay device for causing said display device to display a mark inresponse to each of said first and second marking pulses whereby themark displayed in response to said first marking pulse is indicative ofa particular adjustable preselected distance and the marks displayed inresponse to said second marking pulses are indicative of particularfixed distances.
 2. The apparatus defined in claim 1, wherein saidpreselector means includes digital indicator means for displaying saidpreselected count.
 2. gating means, connected to said primary pulsesource means, for passing said primary pulses upon receipt of a gatingpulse; and
 3. third pulse counter means, connected to said gating means,for producing said timing pulses upon receipt of the mth primary pulsefrom said gating means.
 3. The apparatus defined in claim 1, whereinsaid means for causing said pulse counter to begin counting comprisesmeans, connected to said pulse generator means, for starting said pulsegenerator means each time said position-finding systEm transmits a beampulse.
 4. The apparatus defined in claim 3, wherein saidposition-finding system includes a transmitter means, connected to saidstarting means, for transmitting the beam pulses and wherein saidstarting means synchronously gates said transmitter means and said pulsegenerator means.
 5. The apparatus defined in claim 1, wherein saidposition-finding system includes a transmitter means for transmittingthe beam pulses, and wherein said means for causing said counter meansto begin counting comprises a second pulse counter means, connected tosaid pulse generator means and to said transmitter means, forsynchronously gating said transmitter means upon receipt of the nthtiming pulse from said pulse generator means.
 6. The apparatus definedin claim 1, wherein said timing pulses are spaced with a periodcorresponding to the smallest unit of distance to be displayed on saiddisplay device.
 7. The apparatus defined in claim 1, wherein said pulsegenerator means includes:
 8. The apparatus defined in claim 7, whereinsaid position finding system includes a transmitter means fortransmitting the beam pulses, and wherein said means for causing saidcounter means to begin counting comprises control means, connected tosaid transmitter means and to said gating means, for synchronouslygating said transmitter means and said gating means.